Adaptive transmission device using limited feedback information in a mobile communication system, and a method thereof

ABSTRACT

The present invention relates to an adaptive transmitting device using limited feedback information in a mobile communication system, and a method thereof. According to an exemplary embodiment of the present invention, when the base station transmits a pilot signal to the terminal, the terminal generates channel information by using the pilot signal, generates additional channel information from the channel information, and transmits the channel information and the additional channel information to the base station. The base station determines band allocation, power allocation, and modulation methods for each use by using received feedback information, and transmits modulated traffic data to the terminal according to the determined methods.

TECHNICAL FIELD

The present invention relates to an adaptive transmitting device usinglimited feedback information in a mobile communication system, and amethod thereof. More specifically, the present invention relates to anadaptive transmitting device using limited feedback information in amobile communication system performing adaptive transmission, by usinglocation information and additional information on selected bands whenchannel information on each terminal is transmitted from a mobileterminal to a base station in order to use a downlink adaptivetransmission method in a frequency division multiple access mobilecommunication system.

BACKGROUND ART

To provide mobile communication services to a plurality of users, it isrequired to physically divide communication path capacity. Amultiplexing method and a multiple access method are used to divide thecommunication path capacity. In the multiplexing method, a transmittertransmits a signal in a frequency division multiplexing (FDM) method ora time division multiplexing (TDM) method when a communication path isused between two base stations. Multiple access methods include afrequency division multiple access (FDMA) method, a time divisionmultiple access (TDMA) method, and a code division multiple access(CDMA) method, in which a plurality of terminals use the dividedcommunication path capacity of one base station.

Among these methods, the frequency division multiple access method iswidely used since configurations of antennas, amplification devices, andmodulators are simplified, and there is no need to perform complicatedsynchronization.

FIG. 1 shows a diagram representing a modulation method in aconventional frequency division multiple access mobile communicationsystem.

In the conventional frequency division multiple access mobilecommunication system, a base station 110 includes a band allocator 112for each terminal and a modulator 114 following band allocation to eachterminal, and a terminal 120 includes a receiver 122 and a demodulator124.

A transmitter of the base station 110 transmits modulated data to thereceiver 122 of each terminal 120 through a radio channel, and thereceiver 122 of each terminal 120 restores the data by demodulating themodulated data with the demodulator 124.

However, there is a problem in that performance is reduced since eachterminal has different radio channel performance in the above system.

To solve the above problem, an adaptive transmission method forperforming channel estimation by the terminal 120 has been suggested.

FIG. 2 shows a diagram representing an adaptive transmission method forperforming the channel estimation by the terminal in the frequencydivision multiple access mobile communication system.

In the adaptive transmission method for performing the channelestimation, a base station 210 additionally includes a pilot signalgenerator 212, and a terminal 220 additionally includes a channelestimator 222. The pilot signal generator 212 and the channel estimator222 are not included in the base station of the conventional frequencydivision multiple access method. The receiver 122 of the terminal 220 isnot illustrated in FIG. 2, and will be described assuming that it isincluded in the demodulator 124.

The transmitter of the base station 210 transmits a pilot signal or apreamble to the receiver of each terminal 220 through the radio channel,the receiver of each terminal 220 uses the pilot signal or the preambleto demodulate data with the demodulator 124, and the channel estimator222 for estimating a channel frequency response estimates the channelfrequency response on each band. Subsequently, channel information onevery band is fed back to the base station 210. Then, the band allocator112 for determining a band allocation method for each terminaldetermines a band to be allocated to the terminal 220 based on thereceived channel information. When the band to be allocated to eachterminal is determined, the modulator 114 of each band allocated to eachterminal modulates data, and adaptively transmits traffic data.Accordingly, performance and capacity in the mobile communication systemare increased, which has been suggested in a paper entitled“Computationally Efficient Bandwidth Allocation and Power Control forOFDMA” in IEEE Transaction Wireless Communication Vol. 2 (published 112003).

However, in the above method, since channel information on bands whichare not allocated to the terminal is also required to be fed back to thebase station, overhead of the feedback information is greatly increased,and the receiver of the terminal is required to transmit a large amountof information to the base station. Therefore, the system isdeteriorated since power consumption is increased and interference isgenerated between the terminals. To solve the above problem, a methodfor transmitting channel information on the bands allocated to theterminal rather than transmitting the channel information on all thebands, and reducing the overhead at the base station without performancedegradation, has been suggested in a transaction entitled“‘Opportunistic Scheduling with Partial Channel Information in OFDM/FDDSystems” in IEEE Vehicular Technology Conference Vol. 1 (published 92004). However, in the above method, there is a problem in that adesired bit error rate may not be obtained since an average value ofchannel frequency response values of all the bands is used to performthe modulation for the bands which are not allocated to the terminal.

The above information disclosed in this Background section is only forenhancement of understanding of the background of the invention andtherefore it may contain information that does not form the prior artthat is already known in this country to a person of ordinary skill inthe art.

DISCLOSURE Technical Problem

The present invention has been made in an effort to provide an adaptivetransmitting method for estimating channel frequency response by aterminal by using a pilot signal or a preamble transmitted from a basestation, transmitting frequency responses of selected bands andadditional information for estimating channel information on all bandsfor each terminal to the base station, and performing band allocationfor each terminal based on the frequency responses and the additionalinformation.

Technical Solution

An exemplary adaptive transmission base station for performing adaptiveto transmission by using feedback information transmitted from aterminal in a mobile communication system according to an embodiment ofthe present invention includes a location information storage unit, anadditional information storage unit, a band allocator, a non-allocationband estimation allocator, a band allocation information generator, andan allocated band modulator. The location information storage unitreceives selected band channel location information included in thefeedback information and stores the received information. The additionalinformation storage unit receives additional information from theterminal, the additional information being that for estimating channelswhich are not transmitted, and stores the additional information. Theband allocator allocates a band to each terminal by using the channellocation information and the additional information. The non-allocationband estimation allocator estimates information on empty bands notallocated to the terminal by using the additional information, andallocates the empty bands to the terminal. The band allocationinformation generator generates information on bands allocated to theterminal by the band allocator and the non-allocation band estimationallocator. The allocated band modulator modulates traffic data accordingthe band information, and transmits the modulated traffic data to theterminal.

In an exemplary method for performing adaptive transmission by a basestation by using feedback information transmitted from a terminal in amobile communication system according to an embodiment of the presentinvention, a) channel information and additional information generatedby the terminal are received, b) the channel information and theadditional information are used to estimate a band to be used in theterminal, and the band is allocated to each terminal, c) the additionalinformation is used to generate distance information bands not allocatedto the terminal and the band to be allocated to each terminal, d) thedistance information is used to estimate a channel value of the band notallocated to the terminal, and the band is allocated to the terminal,and e) traffic data are modulated according to the channel informationallocated to the terminal, and the modulated traffic data aretransmitted.

In an exemplary method for performing adaptive transmission by a basestation by using feedback information transmitted from a terminal in amobile communication system according to another embodiment of thepresent invention, a) first feedback information including selected bandchannel location information and additional information is received fromthe terminal, b) the channel location information and the additionalinformation are used to estimate a band to be used in the terminal, andthe band is allocated to each terminal, c) allocated band information istransmitted to the terminal, and allocation band channel informationcorresponding to the band information is received as second feedbackinformation from the terminal, and d) traffic data are modulatedaccording to the received allocation band channel information.

An exemplary terminal performing transmitting feedback information to abase station to perform adaptive communication in a mobile communicationsystem according to an embodiment of the present invention includes achannel estimator, a transmission band selector, a location informationgenerator, and an additional channel information generator. The channelestimator estimates channel information by using a pilot signaltransmitted from the base station. The transmission band selectorselects a band to be transmitted to the base station by using thechannel information. The location information generator generateschannel location information on the selected band. The additionalchannel information generator generates additional channel informationby using the channel information (the additional channel informationtransmitted to estimate non-allocated band in the base station).

In an exemplary method for transmitting feedback information to a basestation to perform adaptive communication by a terminal in a mobilecommunication system according to another embodiment of the presentinvention, a) a pilot signal is received from the base station togenerate channel information on all bands, b) the channel information onall the bands is compared to select a channel of a selected band to betransmitted to the base station, c) channel location information andadditional channel information are generated from the selected channel,and the channel location information and the additional channelinformation are transmitted as first feedback information, d) bandallocation information on bands to be used is received from the basestation, and e) allocation band channel information is generatedaccording to the received band allocation information, and theallocation band channel information as second feedback information istransmitted to the base station.

Advantageous Effects

According to the exemplary embodiment of the present invention, sincethe channel information on the selected bands for each terminal is fedback or the location information on the allocated channels and theaverage information on the channel frequency responses are fed back whenthe frequency division multiple access mobile communication systemperforms the adaptive transmission, overhead occurring in the basestation due to a great deal of information may be reduced, andinterference caused by the transmission information may be reduced atthe terminal.

In addition, when the same amount of information is transmitted to thebase station, the performance in the mobile communication system may beincreased by efficiently performing the band allocation for eachterminal in a system having frequent channel variations, since thesystem transmitting the channel information on the selected bandsaccording to the exemplary embodiment of the present invention transmitsthe channel information more frequently than the conventional system fortransmitting all the bands.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a diagram representing a modulation method in aconventional frequency division multiple access mobile communicationsystem.

FIG. 2 shows a diagram representing an adaptive transmission method forperforming the channel estimation by the terminal in the frequencydivision multiple access mobile communication system.

FIG. 3 shows a diagram representing a band expression in a frequencydivision multiple access mobile communication system.

FIG. 4 shows a diagram representing an adaptive modulation method forperforming the channel estimation by the terminal of the frequencydivision multiple access mobile communication system according to anexemplary embodiment of the present invention.

FIG. 5 a block diagram representing a device for selecting the band tobe transmitted to the base station based on the channel informationestimated by the terminal according to the exemplary embodiment of thepresent invention.

FIG. 6 shows a flowchart representing a method for transmitting thechannel information of the selected band and the additional channelinformation from the terminal to the base station according to theexemplary embodiment of the present invention.

FIG. 7 shows a block diagram representing a base station for allocatingthe bands to the respective terminals based on the channel informationtransmitted from a terminal according to the exemplary embodiment of thepresent invention.

FIG. 8 shows a flowchart representing a method for allocating the bandsto each terminal by using the channel information on the selected bandsaccording to the exemplary embodiment of the present invention.

FIG. 9 shows a diagram representing a method for allocating the band bythe base station by using the channel location information and theadditional channel information received from the terminal according tothe exemplary embodiment of the present invention.

FIG. 10 shows a diagram representing a band allocation method accordingto a passage of time in the frequency division multiple access mobilecommunication system.

FIG. 11 shows a block diagram of an internal configuration of theterminal transmitting the first feedback information, receiving the bandallocation information from the base station, generating the secondfeedback information, and transmitting the second feedback informationto the base station.

FIG. 12 shows a flowchart for representing a method for transmitting thefirst feedback information, receiving the band allocation informationfrom the base station, and transmitting the second feedback informationaccording to the exemplary embodiment of the present invention.

FIG. 13 shows a block diagram of an internal configuration of a basestation receiving the first feedback information from the terminal,allocating the band, receiving the second feedback information, andtransmitting the traffic data according to the exemplary embodiment ofthe present invention.

FIG. 14 shows a flowchart for representing a method for receiving thefirst feedback information from the terminal, allocating the band,receiving the second feedback information, and transmitting the trafficdata according to the exemplary embodiment of the present invention.

FIG. 15 shows a block diagram of an internal configuration of a basestation using the band location information and the additional channelinformation to select terminals receiving the data, and allocating thebands to the selected terminals according to the exemplary embodiment ofthe present invention.

FIG. 16 shows a flowchart for representing a method for using the bandlocation information and the additional channel information to selectthe terminals receiving the data from the base station, and allocate thebands to the selected terminals.

FIG. 17 shows a graph for comparing system performance when the terminaltransmits the channel information on the selected bands to the basestation according to the exemplary embodiment of the present inventionwith system performance when the terminal transmits the channelinformation of all the bands according to the prior art.

FIG. 18 shows a table comparing the amount of information when theterminal transmits the channel information on the selected bands to thebase station according to the exemplary embodiment of the presentinvention, and when the terminal transmits the channel information onall the bands to the base station according to the prior art.

BEST MODE

An exemplary embodiment of the present invention will hereinafter bedescribed in detail with reference to the accompanying drawings.

In the following detailed description, only certain exemplaryembodiments of the present invention have been shown and described,simply by way of illustration. As those skilled in the art wouldrealize, the described embodiments may be modified in various differentways, all without departing from the spirit or scope of the presentinvention. In addition, the drawings and description are to be regardedas illustrative in nature and not restrictive, and like referencenumerals designate like elements throughout the specification.

Throughout this specification and the claims which follow, unlessexplicitly described to the contrary, the word “comprise” or variationssuch as “comprises” or “comprising” will be understood to imply theinclusion of stated elements but not the exclusion of any otherelements.

In addition, the word “module” will be understood to indicate a unit forprocessing a predetermined function or operation, which may be realizedby hardware, software, or a combination thereof.

A downlink frame configuration in a frequency division multiple accessmobile communication system includes a series of slots, and each slotincludes more than one symbol. In addition, the respective slots includepilot signals dispersed at time and frequency domains to estimate achannel, and one slot includes a plurality of data channels

In addition, a receiver estimates the channel by using the pilot signaland transmits the estimated channel back to a base station, and the basestation allocates appropriate bands to respective terminals by usingchannel information estimated for the respective terminals.

According to the prior art, when the respective terminals transmit thechannel information on the respective bands to the base station, thebase station selects a terminal having a lot of channel information toallocate a band to the terminal after comparing the channel informationon the respective terminals in one band. Therefore, the channelinformation on the terminals not selected by the base station is notnecessary. Therefore, when the unnecessary information is reduced, theamount of information transmitted from the respective terminals to thebase station is reduced. However, when the channel information fed backto the base station is reduced as above, it is possible that all theterminals in one band may not transmit the channel information. In thiscase, additional channel information is fed back to the base stationalong with the channel information on the selected bands to allocate theband to the terminals, and bands not allocated to the terminal may beallocated by using the additional channel information. In addition, theterminal estimates the channel and transmits channel locationinformation and the additional channel information on the selected bandsto the base station, and the base station uses the information todetermine the band to be allocated to the respective terminals,transmits the channel information on the bands allocated to therespective terminals, and performs modulation to perform adaptivetransmission.

FIG. 3 shows a diagram representing a band expression in a frequencydivision multiple access mobile communication system.

In the band expression in the frequency division multiple access mobilecommunication system, NM subcarriers are divided into N groups of Msubcarriers to express a band as shown in FIG. 3. In addition, h_(k,1)denotes a frequency response of a first channel of a K^(th) terminal,H_(k,n) denotes a frequency response of a channel of an n^(th) band ofthe K^(th) terminal, and H_(k,n) is shown as Math Figure 1.

$\begin{matrix}{H_{k,n} = {\arg\;{\min\limits_{m}\left\{ {h_{k,{m + {{({n - 1})}M}}}}^{2} \right\}}}} & \left\lbrack {{MathFigure}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Here, m=1:M, and M denotes the number of subcarriers in one band. Afrequency response of a subcarrier, among the respective subcarriers ina band, having a least square value of absolute value of a channelfrequency response is selected as H_(k,n). Since the channel informationtransmitted to the base station by the terminal uses H_(k,n) and areceived signal-to-noise ratio (SNR) is in proportion to H_(k,n), theterminal transmits the channel information to the base to station in thesame manner.

FIG. 4 shows a diagram representing an adaptive modulation method forperforming the channel estimation by the terminal of the frequencydivision multiple access mobile communication system according to anexemplary embodiment of the present invention.

A base station 410 using the adaptive modulation method for performingthe channel estimation by the terminal according to the exemplaryembodiment of the present invention includes a pilot signal generator412, a band allocator 414 for each terminal, and a modulator 416 of eachband allocated to each terminal, and a terminal 420 includes ademodulator 422, a channel estimator 424, and a transmission channelselector 426.

When a pilot signal generated by the pilot signal generator 412 of thebase station 410 is transmitted to the terminal 420, the demodulator 422of the terminal 420 demodulates the pilot signal or a preamble, thechannel estimator 424 estimates a radio channel, and the transmissionchannel selector 426 selects a band to be transmitted to the basestation 410. In addition, the channel information on the band selectedby the terminal 420 is transmitted to the base station 410. The bandallocator 414 of the base station 410 uses the channel informationreceived from the terminal 420 to allocate bands used by the respectiveterminals, and the modulator 416 determines a modulation methodaccording to the channel information on the band allocated to eachterminal and generates traffic data to transmit it to the terminal 420.The demodulator 422 of the terminal 420 demodulates the received trafficdata.

FIG. 5 a block diagram representing a device for selecting the band tobe transmitted to the base station based on the channel informationestimated by the terminal according to the exemplary embodiment of thepresent invention.

A channel estimator 512 of the terminal 510 estimates a channelfrequency response between the base station and the terminal by usingthe received pilot signal.

A transmission band selector 514 transmits selected band channelinformation calculated as Math Figure 2 to the base station by using theestimated channel information.CH _(k)(l)=y _(k)(l)  [Math Figure 2]

Here, i=1:I, and I denotes the number of selected bands transmitted fromthe terminal to the base station. In addition, CH_(k)(i) denotes ani^(th) element of a channel selected to be transmitted from a k^(th)terminal to the base station, y_(k)(i) denotes an i^(th) element of asequence of {H_(k,n)} arranged in descending power, and N denotes thenumber of channels of all the bands between the terminal and the basestation.

In addition, an additional channel information generator 516 generatesadditional channel information representing characteristics of the allchannels by using the channel information from the channel estimator512, and transmits it to the base station. As shown in Math Figure 3,the additional channel information generator 516 generates theadditional channel information to be transmitted to the base station byusing the channel information estimated to by the channel estimator 512(i.e., the additional channel information generator 516 generates thechannel information for estimating the channels not transmitted to thebase station).D _(k)=max(|H _(k,1) −H _(k,2)|,|H_(k,2) −H _(k,3) |, . . . ,|H _(k,N-1)−H _(k,N)|)  [Math Figure 3]

FIG. 6 shows a flowchart representing a method for transmitting thechannel information of the selected band and the additional channelinformation from the terminal to the base station according to theexemplary embodiment of the present invention.

A method for generating the channel information and the additionalchannel information on the selected bands by using the pilot signaltransmitted from the base station to transmit the generated informationto the base station will now be described.

Firstly, the channel estimator 512 of the terminal receives the pilotsignal from the base station, and estimates the channel by using thereceived pilot signal in step S610. When the channel estimation iscompleted, the channel information is found by comparing the channelfrequency responses of all the estimated bands in step S620.

When comparing the channel frequency responses is completed, the channelinformation on bands to be transmitted to the base station is determinedby using the frequency response on the estimated channel. Step S630 fordetermining the channel information may include a step for generatingthe channel information of bands having a higher value to be transmittedto the base station by using the channel information on the bands foundin step S620, and a step for generating channel information estimatingthe channel information on all the bands by using the frequencyresponses of all the band channels.

In addition, differences between values of adjacent channels of all theis bands are found in step S640, and the greatest value among thedifferences is selected to generate the additional channel informationfor estimating the remaining bands in step S650.

When the channel information on the selected bands and the additionalchannel information have been generated in steps S630 to S650, thegenerated information is transmitted to the base station in step S660.

FIG. 7 shows a block diagram representing a base station for allocatingthe bands to the respective terminals based on the channel informationtransmitted from a terminal according to the exemplary embodiment of thepresent invention.

When the channel information and the additional channel information onthe selected bands are transmitted from the terminal as shown in FIG. 6,the base station receives the channel information on the selected bandsthrough a feedback channel information storage unit 712. When thefeedback channel information storage unit 712 receives the channelinformation on the selected band, a band allocator 714 for allocating aband to each terminal by using the channel information generates bandallocation information for allocating the channel information on theselected bands to the terminal. A method for allocating the band to therespective terminals is shown a Math Figure 4.

$\begin{matrix}{{{ChAl}_{i} = {\max\limits_{k}\left( H_{k,i} \right)}}{k^{\prime} = {\arg\;{\max\limits_{k}\left( H_{k,i} \right)}}}{C_{k^{\prime}} = {C_{k^{\prime}}U\left\{ i \right\}}}} & \left\lbrack {{MathFigure}\mspace{14mu} 4} \right\rbrack\end{matrix}$

Here, ChAl_(i) denotes the greatest channel information among thechannel information on all the terminals of an i^(th) band, and C_(k)denotes a band allocated to a k^(th) terminal. In addition, the bandallocator 714 for allocating the band to the respective terminals byusing the channel information transmits information on empty bands notallocated to the terminals to a non-allocated band estimation allocator718.

In addition, an additional channel information storage unit 716 of thebase station stores the additional channel information, and transmitsthe stored additional information to the non-allocated band estimationallocator 718.

The non-allocated band estimation allocator 718, after receiving theadditional information from the additional channel information storageunit 716 and receiving the non-allocated band information from the bandallocator 714, estimates channels as shown in Math Figure 5 by using theselected channel information.

$\begin{matrix}{{{{if}\mspace{14mu}{ChAl}_{i}} = 0}{{{{for}\mspace{14mu} k} = 1};K}{E_{k,i} = {\max\limits_{j}\left( {{{CH}_{k}(j)} - {{\alpha_{k,i}(j)}D_{k}}} \right)}}{end}{{ChAl}_{i} = {\max\limits_{k,{{\#\; C_{k}} < F}}\left( E_{k,i} \right)}}{k^{\prime} = {\arg\;{\max\limits_{k,{{\# C_{k}} < F}}\left( E_{k,i} \right)}}}{C_{k^{\prime}} = {C_{k^{\prime}}U\left\{ i \right\}}}} & \left\lbrack {{MathFigure}\mspace{14mu} 5} \right\rbrack\end{matrix}$

Here, i=1:N, #C_(k) denotes the number of bands allocated to a k^(th)terminal, and F denotes a maximum number of bands allocated to aterminal. In addition, E_(k,i) denotes an estimate value of an i^(th)band channel of the k^(th) terminal, and the estimate value is estimatedby using the channel transmitted from the terminal.

Accordingly, the non-allocated band estimation allocator 718 mayestimate channel information on a desired band by using a distancedifference between the band to be estimated and the additional channelinformation transmitting the greatest value among channel frequencyresponse differences. In addition, a_(k,i(j)) denotes the number ofbands between an i^(th) band to be estimated by a k^(th) terminal and ai^(th) greatest channel transmitted to the terminal.

When the band allocation information is generated as shown in MathFigure 4 and Math Figure 5 as described above, the generated bandallocation information is allocated to the respective terminals. Then,an allocated band modulator 720 for each terminal modulates the bandallocation information and transmits traffic data.

FIG. 8 shows a flowchart representing a method for allocating the bandsto each terminal by using the channel information on the selected bandsaccording to the exemplary embodiment of the present invention.

When the feedback channel information storage unit 712 of the basestation receives the channel information on the selected bands from theterminal, the band allocator 714 for allocating the band to eachterminal by using the received channel information on the selected bandsallocates the bands to the respective terminals in step S810.

The bands other than the bands allocated to the terminals in step S810are allocated to the terminals by using the additional channelinformation. Accordingly, the base station calculates information on adistance between the band not allocated to the terminal and the band towhich the terminal transmits the channel information in step S820, usesthe calculated distance information to estimate the channel informationon the band not allocated to the terminal, and allocates the band to aterminal having a greatest channel frequency response in step S830.

In addition, the band allocation information allocated to the respectiveterminals in steps S810 to S830 is modulated by a modulator, and thetraffic data are transmitted to the respective terminals in step S840.

FIG. 9 shows a diagram representing a method for allocating the band bythe base station by using the channel location information and theadditional channel information received from the terminal according tothe exemplary embodiment of the present invention.

A base station 910 according to the exemplary embodiment of the presentinvention includes a pilot signal generator 912, a band allocator 914for each terminal, a band location information transmitter 916, and amodulator 918, and a terminal 920 includes a demodulator 922, a channelestimator 924, and a transmission channel selector 926.

The demodulator 922 of the terminal 920 receives a pilot signalgenerated by the pilot signal generator 912 of the base station 910 anddemodulates the generated pilot signal, and the channel estimator 924estimates a radio channel. When the channels of all the bands areestimated by the channel estimator 924, the transmission channelselector 926 selects the channel to be transmitted to the base station910, and transmits the location band information on the channel selectedby the transmission channel selector 926. The band allocator 914 foreach terminal uses the transmitted channel location information toallocate the band of the channels for the respective terminals, and theband location information transmitter 916 transmits band locations forthe respective terminals by using the allocated band locationinformation. When the demodulator 922 of the terminal 920 demodulatesthe transmitted band location information, the channel estimator 924transmits the channel information on the selected bands to the basestation 910. The modulator 918 for receiving the channel informationmodulates the traffic data to transmit it to the terminal 920.

FIG. 10 shows a diagram representing a band allocation method accordingto a passage of time in the frequency division multiple access mobilecommunication system.

In the conventional band allocation method, when a band is allocated,the channel information of selected bands is fed back to the basestation so that the base station performs band allocation for eachterminal, and the base station performs modulation and power allocationto transmit the traffic data to the terminal according to the result ofthe band allocation. However, according to the exemplary embodiment ofthe present invention, when the terminal transmits the band locationinformation on the selected band and the additional channel informationwhich is first feedback information to the base station before the bandis allocated, the base station allocates the band based on theinformation and transmits the allocated band information to theterminal. When the terminal transmits second feedback information, whichis the channel information on the allocated band, to the base stationaccording to the transmitted band information, the base station performsthe modulation and power allocation, which is shown in FIG. 10.

FIG. 11 shows a block diagram of an internal configuration of theterminal transmitting the first feedback information, receiving the bandallocation information from the base station, generating the secondfeedback information, and transmitting the second feedback informationto the base station.

A terminal 1100 according to the exemplary embodiment of the presentinvention uses a pilot signal transmitted from the base station toestimate the channel frequency responses of all the bands by a channelestimator 1102. After the response estimation, a transmission bandselector 1104 uses the estimated channel information to select thechannel to be transmitted to the base station, and a locationinformation generator 1106 generates the location information on thechannels of the selected bands. The generated channel locationinformation U_(k(j)) indicates a frequency band location of y_(k(j)),and the location information generator 1106 transmits the generatedU_(k)={U_(k) 1, U_(k) 2, . . . , U_(k)(I)} to the base station.

In addition, an additional channel information generator 1108 generatesadditional information including an average value of the channelinformation on the band transmitted to the base station as shown in MathFigure 6, and transmits the additional information to the base stationto estimate and select the rest of the bands.

$\begin{matrix}{{AVE}_{k} = {\frac{1}{l}{\sum\limits_{i = 1}^{l}{{CH}_{k}(i)}}}} & \left\lbrack {{MathFigure}\mspace{14mu} 6} \right\rbrack\end{matrix}$

When the base station performs the band allocation by using the selectedband channel location information which is the first feedbackinformation and the additional channel information, and transmits theallocated band, the channel estimator 1102 of the terminal 1100 receivesthe allocated band and an allocation band channel information generator1110 generates allocation band channel information which is the secondfeedback information so as to transmit the generated allocation bandchannel information back to the base station.

FIG. 12 shows a flowchart for representing a method for transmitting thefirst feedback information, receiving the band allocation informationfrom the base station, and transmitting the second feedback informationaccording to the exemplary embodiment of the present invention.

The channel estimator 1102 of the terminal estimates the channel in stepS1210 by using the pilot signal received from the base station. Thetransmission band selector 1104 compares the channel information on theestimated bands in step S1220 to select the band having the greatchannel frequency response as the channel of the band to be transmittedto the base station in step S1230.

When the channel is selected, the channel is expressed as bits to beadaptively transmitted to the base station. Accordingly, the locationinformation generator 1106 generates the location information on thechannels selected to be transmitted to the base station in step S1240,and the additional channel information generator 1108 calculates anaverage value of the selected channels to generate the additionalchannel information in step S1250.

When the selected channel information and the additional channelinformation are generated, the terminal transmits the information to thebase station in step S1260 and receives information on bands to be usedfrom the base station in step S1270. The terminal generates the channelinformation in step S1280 according to the band allocation informationreceived from the base station, and expresses the channel information onthe allocated band as bits to be transmitted to the base station in stepS1290.

FIG. 13 shows a block diagram of an internal configuration of a basestation receiving the first feedback information from the terminal,allocating the band, receiving the second feedback information, andtransmitting the traffic data according to the exemplary embodiment ofthe present invention.

The base station according to the exemplary embodiment of the presentinvention includes a location information storage unit 1302 for storinglocation information on the selected band channels fed back from theterminal, an additional information storage unit 1304 for storingadditional information on the channel fed back from the terminal, a bandallocator 1306 for allocating a band to each terminal by using thechannel location information and the additional information, anon-allocated band estimation allocator 1308 for allocating bands nottransmitted by the terminal to each terminal, a band allocationinformation generator 1310 for generating information on the allocatedband, and an allocated band modulator 1312 for receiving the secondfeedback information and modulating the received second feedbackinformation to transmit it to the terminal.

The band allocator 1306 for receiving the second feedback information iswhich is the location information on the selected bands and theadditional information allocates the bands for the respective terminalsas shown in Math Figure 7.

$\begin{matrix}{\left. P\leftarrow{1 \times N\mspace{14mu}{zero}\mspace{14mu}{vector}} \right.{U = \phi}{{{for}\mspace{14mu} l} = {1\text{:}K_{cell}}}{M = {\left\{ {1,L,K_{cell}} \right\} - U}}{k = {\arg\;{\max\limits_{m \in M}\left( {AVE}_{m} \right)}}}{{{for}\mspace{14mu} n} = {1:N}}{{{if}\mspace{14mu}{P_{k}(n)}} = {{1\mspace{14mu}{and}\mspace{14mu}{P(n)}} = {{0\mspace{14mu}{and}\mspace{14mu}\# C_{k}} < F}}}{C_{k} = {C_{k}U\left\{ n \right\}}}{{P(n)} = 1}{end}{U = {U\; U\left\{ k \right\}}}{end}} & \left\lbrack {{MathFigure}\mspace{14mu} 7} \right\rbrack\end{matrix}$

Here, P denotes a 1×N vector, P_(k) denotes a 1×N vector in whichU_(k)(1)^(th), U_(k)(2)^(th), . . . , and U_(k)(I)^(th) elements are 1and the other elements are 0, K_(cell) denotes the number of terminalsselected by the base station, P(n) denotes an n^(th) element of a Pvector, and P_(k)(n) denotes an n^(th) element of a P_(k) vector.

In addition, after the band allocator 1306 allocates the band, and thenon-allocated band estimation allocator 1308 for allocating bands thatare not transmitted allocates the remaining bands to each terminal asshown in Math Figure 8.

$\begin{matrix}{\mspace{79mu}{{i = 1}\mspace{20mu}{{{for}\mspace{14mu} n} = {1\text{:}N}}\mspace{20mu}{{{if}\mspace{14mu}{P(n)}} = 0}\mspace{20mu}{while}{Q_{n} = \left\{ {\left. k \middle| {P_{k}\left( {n - i} \right)} \right. = {{1\mspace{14mu}{or}\mspace{11mu}{P_{k}\left( {n + i} \right)}} = {{1\mspace{14mu}{and}\mspace{14mu}\# C_{k}} < F}}} \right\}}\mspace{20mu}{{if}\mspace{14mu} Q_{n}\mspace{14mu}{not}\mspace{14mu}{empty}}\mspace{20mu}{k^{\prime} = {\arg\;{\max\limits_{k \in Q_{n}}\left( {AVE}_{k} \right)}}}\mspace{20mu}{break}\mspace{20mu}{else}\mspace{20mu}{i = {i + 1}}\mspace{20mu}{end}\mspace{20mu}{C_{k^{\prime}} = {C_{k^{\prime}}U\left\{ n \right\}}}}} & \left\lbrack {{MathFigure}\mspace{14mu} 8} \right\rbrack\end{matrix}$

When the band allocation for each terminal is completed by using MathFigure 7 and Math Figure 8, the band allocation information generator1310 transmits the allocated band information to the respectiveterminals.

FIG. 14 shows a flowchart for representing a method for receiving thefirst feedback information from the terminal, allocating the band,receiving the second feedback information, and transmitting the trafficdata according to the exemplary embodiment of the present invention.

The base station receives the first feedback information which is thechannel information on the selected bands for the respective terminalsand the additional channel information which is an average of thechannel information of the selected bands in step S1410. In addition,the band allocator 1306 uses the channel information on the selectedbands and the additional channel information to allocate the bands tothe respective terminals in step S1420, and is the non-allocated bandestimation allocator 1308 uses the additional channel information toallocate the remaining bands to the terminals in step S1430.

In addition, the base station transmits the allocated band informationto the respective terminals in step S1440, and receives the allocationband channel information transmitted by the respective terminals as thesecond feedback information in step S1450. The base station receivingthe second feedback information modulates the allocation band channelinformation transmitted by the terminal in step S1460, and transmits thetraffic data to the respective terminals in step S1470.

Accordingly, when the base station receives the location information onthe selected bands and the additional channel information from theterminal, the base station uses the location information to allocate thebands to the respective terminals, uses the additional information toallocate the bands not allocated to the respective terminals, transmitsthe band location information to the respective terminals, receives thechannel information on the allocated bands from the respectiveterminals, modulates the channel information, and transmits the trafficdata.

FIG. 15 shows a block diagram of an internal configuration of a basestation using the band location information and the additional channelinformation to select terminals receiving the data, and allocating thebands to the selected terminals according to the exemplary embodiment ofthe present invention.

The diagram of the base station shown in FIG. 15 is a detailed diagramof the base station shown in FIG. 13, and the base station shown in FIG.15 further includes a terminal selector 1502, a selected terminallocation information storage unit 1504, and a selected terminaladditional information storage unit 1506. The terminal selector 1502uses the selected band channel location information received from thelocation information storage unit 1302 and the additional informationreceived from the additional information storage unit 1304 to select theterminal to which the band is allocated.

The terminal selector 1502 uses the channel information stored in thelocation information storage unit 1302 and the additional informationstorage unit 1304 to select the terminal receiving the data from thebase station. The terminal is selected as shown in Math Figure 9.

$\begin{matrix}{{N_{UE} = 1}{u = {\arg\;{\max\limits_{k}\left( {AVE}_{k} \right)}}}{P = P_{u}}{U_{N_{UE}} = \left\{ u \right\}}{{{while}\mspace{14mu} N_{UE}} < {K_{cell}\mspace{14mu}{do}}}{k \in {\left\{ {1,L,K} \right\} - U_{N_{UE}}}}{{Cost}_{k} = {\begin{pmatrix}{{A\left( {P_{k} - P} \right)} +} \\{\beta\left( {N - {A\left( {P_{k} + P} \right)}} \right)}\end{pmatrix} \times \left( {AVE}_{k} \right)}}{l = {\arg\;{\max\left( {Cost}_{k} \right)}}}{N_{UE} = {N_{UE} + 1}}{U_{N_{UE}} = {U_{N_{UE}}U\left\{ l \right\}}}{P = {P \oplus P_{l}}}{end}} & \left\lbrack {{MathFigure}\mspace{14mu} 9} \right\rbrack\end{matrix}$

Here, U_(NUE) denotes a terminal selected by the base station, Cost_(k)denotes a Cost function of a k^(th) terminal, and A(P) denotes thenumber of elements of a vector P, the number of elements being greaterthan 0. In addition, β is an empty band allocation coefficient which isestablished as a value between 0 and 1, and {circle around (+)} denotesan OR operation.

When the terminal selector 1502 selects the terminal to which the bandis allocated, the band allocator 1306 for each terminal uses the channellocation information on the selected bands and the additional channelinformation generated by using Math Figure 7 so as to allocate the band,and the non-allocated band estimation allocator 1308 finds the bands notallocated by using Math Figure 8 to allocate the non-allocated bands tothe respective terminals. Then, the band allocation informationgenerator 1310 transmits the allocated band location information to theselected terminals, and receives the terminal allocation band channelinformation which is the second feedback information, and the allocatedband modulator 1312 modulates the received terminal allocation bandchannel information and transmits the traffic data to the terminal.

FIG. 16 shows a flowchart for representing a method for using the bandlocation information and the additional channel information to selectthe terminals receiving the data from the base station, and allocate thebands to the selected terminals.

The base station receives the channel location information on theselected bands for the respective terminals and the additional channelinformation which is the average of the channel information of theselected bands in step S1610, and uses the Cost function of Math Figure9 to select the terminal receiving the data in step S1620.

When the terminal receiving the data is selected, the base station usesthe channel information transmitted from the terminal to allocate theband to be used by the terminal in step S1630, and uses the additionalinformation to allocate the remaining bands to the terminals in stepS1640.

When the channel information is allocated to the respective terminals,the base station transmits the band allocation information to therespective terminals in step S1650. The terminal receiving the bandallocation information generates the channel information on the bands tobe used by the terminals, and transmits the channel information to thebase station. The base station receives the channel information on thebands to be used (i.e., the allocation band channel information which isthe second feedback information) in step S1660, modulates the receivedallocation band channel information in step S1670, and transmits thetraffic data to the respective terminals in step S1680.

FIG. 17 shows a graph for comparing system performance when the terminaltransmits the channel information on the selected bands to the basestation according to the exemplary embodiment of the present inventionwith system performance when the terminal transmits the channelinformation of all the bands according to the prior art.

The graph compares the system performance between the frequency divisionmultiple access mobile communication system transmitting all the bandsand the frequency division multiple access mobile communication systemtransmitting the selected bands (8.3% of all the bands) according to theexemplary embodiment of the present invention. In FIG. 17, FBF denotes amethod for transmitting the channel information on all the bands to thebase station and performing the band allocation for each terminal, andPBSF denotes a method for transmitting the selected band channellocation information and the additional channel information as the firstfeedback information to the base station, and transmitting theallocation band channel information as the second feedback informationto the base station after the base station performs the band allocationfor each terminal and transmits the allocation information to theterminal.

PBDF and PBAF are adaptive transmitting methods for transmitting thechannel information on the selected bands and the additional channelinformation to the base station. In further detail, the PBDF is a methodfor transmitting the additional channel information including a channelinformation difference between neighboring bands, and the PBAF is amethod for transmitting average information on all the bands to the basestation.

As shown in the FIG. 17, the performance degradation in the PBSF, PBDF,and PBAF transmitting the channel information on the selected bandsaccording to the exemplary embodiment of the present invention isreduced compared to the FBF transmitting the channel information on allthe bands according to the prior art.

FIG. 18 shows a table comparing the amount of information when theterminal transmits the channel information on the selected bands to thebase station according to the exemplary embodiment of the presentinvention, and when the terminal transmits the channel information onall the bands to the base station according to the prior art.

In FIG. 18, the table compares the amount of information between thefrequency division multiple access mobile communication systemtransmitting all the bands and the frequency division multiple accessmobile communication system transmitting the selected bands (8.3% of allthe bands) according to the exemplary embodiment of the presentinvention.

As shown in FIG. 18, when a mobile communication system having a totalband of 96 channels, the allocated band of 8 channels for each terminal,5 bits for each channel, and band location information of 7 bits foreach channel transmits all the bands, the number of required bits is480. In addition, when the selected bands are transmitted according tothe exemplary embodiment of the present invention, 21% of bits used inthe conventional communication system may be used since 101 bits arerequired to perform the transmission. As described above, since the bandinformation is transmitted by using fewer bits, the overhead occurringin the base station may be reduced.

The above described methods and apparatuses are not only realized by theexemplary embodiment of the present invention, but, on the contrary, areintended to be realized by a program for realizing functionscorresponding to the configuration of the exemplary embodiment of thepresent invention or a recoding medium for recoding the program.

While this invention has been described in connection with what ispresently considered to be practical exemplary embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments, but, on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

According to the exemplary embodiment of the present invention, sincethe channel information on the selected bands for each terminal is fedback to the base station or the location information on the allocatedchannels and the average information on the channel frequency responsesare fed back to the base station when the frequency division multipleaccess mobile communication system performs the adaptive transmission,the overhead occurring in the base station due to a lot of informationmay be reduced, and the interference caused by the transmissioninformation may be reduced at the terminal.

In addition, according to the exemplary embodiment of the presentinvention, when the same amount of information is transmitted to thebase station, the performance in the mobile communication system may beincreased by efficiently performing the band allocation for eachterminal in a system having frequent channel variations, since thesystem transmitting the channel information on the selected bandsaccording to the exemplary embodiment of the present invention transmitsthe channel information more frequently than the conventional systemthat transmits all the bands.

The invention claimed is:
 1. A method for transmitting feedbackinformation to a base station to perform adaptive communication by aterminal in a mobile communication system, the method comprising: a)receiving a pilot signal from the base station to generate channelinformation on bands; b) comparing the channel information on the bandsto select a channel of a selected band to be transmitted to the basestation; c) generating channel location information and additionalchannel information from the selected channel, and transmitting thechannel location information and the additional channel information asfirst feedback information to the base station; d) receiving bandallocation information on bands to be used from the base station; and e)generating allocation band channel information corresponding to thereceived band allocation information, and transmitting the allocationband channel information as second feedback information to the basestation.
 2. A method for a terminal to transmit information on a channelincluding N bands to a base station, wherein N is a natural number, themethod comprising: selecting m band(s) among the entire N bands, whereinm is a natural number and is less than N; calculating one channelquality information that represents channel quality of the entire Nbands; and transmitting, to the base station, a channel qualityinformation of the selected m band(s), channel location information ofthe selected m band(s), and the one channel quality information thatrepresents channel quality of the entire N bands.
 3. The method of claim2, wherein the terminal selects the m band(s) among the entire N bandsbased on channel quality information estimated by using a pilot signaltransmitted from the base station.
 4. The method of claim 2, wherein thebit length of the one channel quality information that representschannel quality of the entire N bands is less than the bit length ofinformation comprising each individual channel quality information ofthe N bands.